1. Field of the Invention
The present invention relates to a liquid crystal display device with excellent visibility, which prevents light from leaking out from the periphery of a liquid crystal panel in its negative type display. More particularly, the present invention relates to a liquid crystal display device which prevents light leaking out from each of liquid crystal panels e.g. where a large number of the liquid crystal panels are arranged to constitute a large-scale display, thereby increasing the visibility.
2. Description of the Related Art
A liquid crystal display device is structured so that a liquid crystal layer is sandwiched by two insulating plates and polarization plates are arranged on the outer surfaces of the two insulating plates, respectively. In the liquid crystal display device, a voltage can be applied to the liquid crystal layer through electrode patterns provided on the inner surfaces of the insulating plates so that the display can be made by controlling the voltage to be applied. More specifically, when the voltage is not applied to the liquid crystal layer, using the optical rotation property of the liquid crystal layer, linear polarized light having only a fixed vibrating direction is optically-rotated by the one polarizing plate by a certain angle. In this case, if the direction of the rotated linear polarized light coincides with that of the polarizing axis of the other polarizing plate, light passes through the liquid crystal layer, whereas if not, the light does not pass therethrough. On the other hand, when the voltage is applied to the liquid crystal layer, the linear polarized light is not optically rotated. In this way, whether or not the light passes can be controlled whether or not the voltage is applied. Thus, by controlling the voltage for each pixel, desired display can be realized. xe2x80x9cNegative-type displayxe2x80x9d refers to the case where both polarizing plates are arranged so that light does not pass when the voltage is not applied to the liquid crystal layer. xe2x80x9cPositive-type displayxe2x80x9d refers to the case where the light passes when the voltage is not applied so that only the pixel to which a voltage is applied is displayed in black.
In the negative type display, in the state where the liquid crystal panel is not operated, the entire face of the liquid crystal panel exhibits a black image. However, as shown in FIG. 11, in the area of a liquid crystal panel 20 to which sealant 27 is bonded and its outer periphery, liquid crystal is not located. Therefore, epoxy resin which is a sealant and a spacer which is mixed to make the gap uniform transmit light so that the light is not entirely optically rotated even with the provision of the polarizing plates on both sides. Thus, as shown in FIG. 11, although the inside of the sealant 27 where the liquid crystal layer is located exhibits a black image (shaded xe2x80x9cBxe2x80x9d area), light leaks from the periphery. This makes the image very poor. Particularly, in the liquid crystal panel for color display, which is generally in a negative-type display, such a tendency is remarkable.
In a larger-scale display composed of a number of liquid crystal panels, light leaks from the joints therebetween. This makes the image poor in continuous display. In order to overcome such an inconvenience, as shown in FIG. 12, a light shielding tape 28 such as a black vinyl tape is bonded to each joint. The problem relative to the joints occurs not only in the negative display but also in the positive display. Namely, the sealant portion which is black becomes white if no polarized plate is located on the outside thereof.
However, where the light shielding tape 28 is bonded to the joint, discrepancy in position is apt to occur. Therefore, on the display portion onto which the tape is bonded, some breaks may be generated. Otherwise, on the peripheral portion, the leakage of light cannot be prevented completely. In addition, after the liquid crystal panels 20 have been arranged, it is difficult to bond the light shielding tape onto the joints. Further, where a single liquid crystal panel is replaced by another one afterwards, the light shielding tape 28 must be peeled off and thereafter a new light shielding tape must be bonded again. This is very troublesome.
The present invention has been accomplished in order to solve such a problem. The present invention intends to provide a liquid crystal display device which can remove leakage of light from a sealant portion in a negative-type display to improve the appearance of an image. Where a large-scale display is composed of a large number of liquid crystal display devices, the present invention also intends to provide the liquid crystal display device which can surely make light-proof to the joints to constitute such a large-scale display with an excellent display characteristic.
A liquid crystal display device according to the present invention comprises a liquid crystal panel including two insulating base plates with electrode patterns provided on their surfaces, respectively, a sealant which bonds the two insulating base plates to each other at their peripheries with a prescribed gap therebetween so that the electrode patterns are opposite to each other, a liquid crystal layer provided in the prescribed gap between said two insulating base plates, and polarizing plates provided on the outer surfaces of said two insulating base plates, respectively; and a light-shielding mask which is fit in an exterior area from the sealant at an edge of said liquid crystal panel so that it sandwiches said insulating base plates of said liquid crystal panel from both sides.
In this configuration, regardless with the combination of polarizing plates, leakage of light is always eliminated at the portion of the sealant and its exterior, thereby preventing reduction of visibility due to the sealant. As a result, where a plurality of liquid crystal panels are arranged to constitute a large-scale display, it is possible to prevent leakage of light from the joints between the liquid crystal panels without bonding light shielding tapes to the joints.
The light-shielding mask has a U-shape in section formed by bending a metallic plate having a light-shielding property and resiliency and having an opening which has an interval slightly smaller than the thickness of the said liquid crystal panel. In this configuration, the light-shielding mask has only to be fit in order to realize light interruption. Since the light-shielding mask can be formed to have a very small thickness, the interval of each joint can be reduced, thereby realizing continuous display.
If the light-shielding mask is made from a heat-shrinkable tube of color preventing light from being interrupted, a half part cut in an axial direction from the heat-shrinkable tube having a slightly large diameter is covered on the liquid crystal panel and heated to be hardened. This simply realizes light interruption.
A first aspect of the present invention is a liquid crystal display device which comprises:
a liquid crystal panel including two insulating base plates with electrode patterns provided on their surfaces, respectively, a sealant which bonds the two insulating base plates to each other at their peripheries with a prescribed gap therebetween so that the electrode patterns are opposite to each other, and a liquid crystal layer provided in the prescribed gap between said two insulating base plates; and
a light-shielding mask which is fit in an outer periphery of the sealant at an end of said liquid crystal panel so that it sandwiches said insulating base plates of said liquid crystal panel from both sides.
A second aspect of the device is a liquid crystal display device according to the first aspect, wherein the inner edge of said light-shielding mask is substantially aligned with that of the sealant for the liquid crystal panel.
A third aspect of the device is a liquid crystal display device according to the first aspect, wherein said liquid crystal panel further comprises polarized plates provided outside said first and second insulating base plates, respectively.
A fourth aspect of the device is liquid crystal display device according to the first aspect, wherein said light-shielding mask is formed so that said first and second base plates are fit from both sides.
A fifth aspect of the device is liquid crystal display device according to the first aspect, wherein said light-shielding mask has a U-shape in section formed by bending a metallic plate having a light-shielding property and resiliency and having an opening which has an interval slightly smaller than the thickness of the said liquid crystal panel.
A sixth aspect of the device is liquid crystal display device according to the first aspect, wherein said light-shielding mask is made from a heat-shrinkable tube of color preventing light from being interrupted.
A seventh aspect of the device is liquid crystal display device according to the first aspect, wherein said light-shielding mask is provided on each of both opposite sides of the outer periphery of said liquid crystal panel.
An eighth aspect of the device is liquid crystal display device according to the first aspect, wherein said light-shielding mask is provided on each of both opposite sides of the outer periphery of said liquid crystal panel, and on one side located between both opposite sides.
A ninth aspect of the device is liquid crystal display device according to the first aspect, wherein said light-shielding mask is provided to cover the entire outer periphery of said liquid crystal panel.
A tenth aspect of the device is liquid crystal display device according to the first aspect, wherein said light-shielding mask is provided with a light-shielding piece on at least one side thereof, said light-shielding piece extending outward from the outer edge thereof and serving to interrupt external light from the outer edge of said liquid crystal panel.
An eleventh aspect of the device is liquid crystal display device according to the first aspect, wherein said light-shielding mask is provided on the outer periphery of said liquid crystal panel and at a coupling portion of two adjacent liquid crystal panels so that said base plates are fit from its both sides.
A twelfth aspect of the device is liquid crystal display device according to the first aspect, wherein said light-shielding mask includes two light-shielding springs members each having an opening formed in a U-shape in section so as to provide a diameter slightly smaller than the thickness of said liquid crystal panel, said light-shielding spring members being coupled with each other so that their openings are located outside, and two liquid crystal panels are inserted into the corresponding two openings.
A thirteenth aspect of the method is a method of manufacturing a liquid crystal display device, which comprises the steps of:
preparing a liquid crystal panel including two insulating base plates with electrode patterns provided on their surfaces, respectively, a sealant which bonds the two insulating base plates to each other at their peripheries with a prescribed gap therebetween so that the electrode patterns are opposite to each other, and a liquid crystal layer provided in the prescribed gap between said two insulating base plates; and
fixing a light-shielding mask which is fit in an outer periphery of the sealant at an end of said liquid crystal panel so that it sandwiches said insulating base plates of said liquid crystal panel from both sides.
A fourteenth aspect of the method is a method of manufacturing a liquid crystal display device according to the thirteenth aspect, wherein said step of fixing the light-shielding mask comprises the steps:
mounting a resilient light shielding tube so that it sandwiches the insulating base plates of said liquid crystal panel from both sides; and
heating said light-shielding tube so that it is fit on an outer periphery of the sealant at an end of said liquid crystal panel by heat-shrinkage.
A fifteenth aspect of the method is a method of manufacturing a liquid crystal display device according to the thirteenth aspect, wherein said step of fixing the light-shielding mask comprises the step of:
mounting the insulating base plates of said liquid crystal panel into an opening of a light-shielding spring member formed in a U-shape in section so as to provide a diameter slightly smaller than the thickness of said liquid crystal panel so that the insulating base plates are sandwiched by the light-shielding spring member from both sides.
A sixteenth aspect of the method is a method of manufacturing a liquid crystal display device according to the thirteenth aspect, wherein said light-shielding mask is made of a heat-shrinkable tube of color preventing light from being interrupted.
A seventeenth aspect of the method is a method of manufacturing a liquid crystal display device according to the thirteenth aspect, wherein said light-shielding mask is provided on each of both opposite sides of the outer periphery of said liquid crystal panel.
An eighteenth aspect of the method is a method of manufacturing a liquid crystal display device according to the thirteenth aspect,, wherein said step of fixing the light-shielding mask comprises the step of:
mounting said light-shielding mask on the outer periphery of said liquid crystal panel and at a coupling portion of two adjacent liquid crystal panels so that said base plates are fit from its both sides, thereby coupling the two adjacent liquid crystal panels.
A nineteenth aspect of the method is a method of manufacturing a liquid crystal display device according to the fourteenth aspect, wherein said step of fixing the light-shielding mask comprises the step of:
preparing an integral light-shielding mask composed of two light-shielding springs members each having an opening formed in a U-shape in section so as to provide a diameter slightly smaller than the thickness of said liquid crystal, said light-shielding spring members being coupled with each other so that their openings are located outside;
inserting two liquid crystal panels into the corresponding two openings so that they are coupled with each other.